1. Field of the Invention
This invention relates to polystyrene compositions with excellent antistatic properties.
2. Description of the Prior Art
Styrene polymers and copolymers are used as packaging containers for their ease of molding and fabrication. Some of them, such as polystyrene, styrene-butadiene block copolymers, styrene-acrylonitrile copolymers, and styrene-methyl methacrylate copolymers are highly transparent and are used in a variety of packaging containers where transparency counts.
These styrene polymers and copolymers, however, are themselves insulators which tend to accumulate static charges; hence, they have disadvantages that they tend to attract dust or produce arcing to persons touching them.
Of the methods hitherto practiced to overcome such disadvantages, one is to coat or impregnate the articles made from styrene polymers and copolymers with antistatic agents and another is to incorporate antistatic agents mechanically into these styrene polymers and copolymers.
The former method produces an excellent antistatic effect, but the antistatic agent on the surface comes off when the surface is polished or washed. Therefore, a problem with the method is a lack of prolonged antistatic effect and another is poor resistance to water washing. Moreover, an extra operation, at additional cost, of coating or impregnating the articles with antistatic agents becomes necessary.
The latter method can exhibit an antistatic performance which is long-lasting and unaffected by water washing. On the other hand, the antistatic agent incorporated into the polymers sometimes bleeds out to mar the surface. This becomes a serious problem particularly in the cases where the polymers are applied to packaging containers in which the transparency counts.
For inhibition of the blooming, a number of proposals have been made on the use of the following additives: nonionic antistatic agents of high molecular weights, amphoteric antistatic agents, and metal-anionic antistatic agent adducts; ethoxylated amines as antistatic agents (U.S. Pat. No. 4,393,176); organic antistatic agents such as amines, amides, esters, and alcohols in combination with lithium compounds [Japanese Patent Laid open No. 60-44536 (1985)].
The addition of these antistatic agents as proposed, however, is expected to be not very effective with polystyrenes for producing a strong antistatic effect and inhibiting the blooming over an extended period of time and much less effective against rubber-modified polystyrenes.